1

I created a custom CRS for a project I am working on. I then started a new project, set to my custom CRS and turn on "on the fly" transformation. I import Rail data that I know is in my custom CRS, and it imports as expected. However when I import Road data from our library that is in a different CRS, this data goes to a totally different area.

I tried the reverse situation. I opened the Road data in a new project, set the CRS to this layer and turn on "on the fly" transformation. When I import the Rail data (which is in my custom CRS) it imports fine.

I would appreciate your guidance on:

  1. Is it possible to create a project based on a Custom CRS?
  2. Any tricks/tips when importing data and converting it.

Ultimately I want to import the data I am interested in, convert it to my custom CRS so I can test out some of the grass functions (which I understand needs to be in the same CRS), and use qconsolidate to store it is a separate location.

2

I suggest to change your settings under Settings -> Options, CRS, CRS for new layers to Prompt for CRS

You can rightclick on every layer -> Set CRS for Layer and check that your rail data has the custom CRS, but road data another CRS as stated for your library.

If the data comes as shapefiles, they should have the correct .prj file with projection information. CSV files are usually imported into the project CRS, unless you change the preferences as mentioned above.

If you are unsure which data is correct, change the project CRS to EPSG:3857, and load Openstreetmap or Google layer with the Openlayers plugin as background to see which layer fits to that.

Once you are sure that all layers are correct, you can rightclick -> Save As ... to your custom CRS, add that file as new layer, delete the old layer and the Openlayers layers, and change project CRS back to your custom CRS.

If all layers have the same CRS, you can uncheck On-the-fly-reprojection, and the layers should remain in their places.


Below you see a comparison of the different Australian Datum systems at a scale of 1:2000:

enter image description here

Green grid lines are WGS84 (equvalent to GGA94), red is AGD66 with

+proj=longlat +ellps=aust_SA +towgs84=-117.808,-51.536,137.784,0.303,0.446,0.234,-0.29 +no_defs

and blue one is AGD84 with

+proj=longlat +ellps=aust_SA +towgs84=-134,-48,149,0,0,0,0 +no_defs

The green grid is 168m south and 122 metres west of the other two. Red and blue are just 1 meter apart. These offsets may vary across the continent.

  • Thanks Andre, I tried these suggestions but I couldn't get it to work. I think I am doing something incorrect whereby my custom data is in metres, but my other data defaults to longitude/latitude - it always seems to import at the origin. – boberdorf Apr 2 '14 at 11:36
  • With lon/lat coordinates, the CRS of the other data has to be EPSG:4326, so it has to go in a separate layer. How does your custom CRS definition look like? – AndreJ Apr 2 '14 at 11:42
  • My custom CRS is similar to below, but with a different Lon_0 as my site is in a different zone. I bring the other data in by the "Add vector layer" command. +proj=tmerc +lat_0=0 +lon_0=141 +k_0=0.999940 +x_0=300000.000000 +y_0=5000000.000000 +ellps=ANS +a=6378160.0 +b=6356774.719 +f=298.25 +units=m +no_defs no_defs <> – boberdorf Apr 2 '14 at 12:01
  • The ellipsoid shoud be aust_SA, you can ommit a,b and f then. Is your other data a shapefile? Does it have the right .prj file? You can look into that with any text editor. – AndreJ Apr 2 '14 at 12:17
  • I will try changing the ellipsoid tonight. My data has the following PRJ info for the Road Layer I am interested. (GEOGCS["GCS_GDA_1994",DATUM["D_GDA_1994",SPHEROID["GRS_1980",6378137,298.257222101]],PRIMEM["Greenwich",0],UNIT["Degree",0.0174532925199433]]) – boberdorf Apr 3 '14 at 0:30

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